Even if its primary use is for extended scopes in a web environment,
this SPI is completely generic: It provides the ability to get and put
objects from any underlying storage mechanism, such as an HTTP session
or a custom conversation mechanism. The name passed into this class's
get and remove methods will identify the
target object in the current scope.

Scope implementations are expected to be thread-safe.
One Scope instance can be used with multiple bean factories
at the same time, if desired (unless it explicitly wants to be aware of
the containing BeanFactory), with any number of threads accessing
the Scope concurrently from any number of factories.

Register a callback to be executed on destruction of the specified
object in the scope (or at destruction of the entire scope, if the
scope does not destroy individual objects but rather only terminates
in its entirety).

Method Detail

get

Return the object with the given name from the underlying scope,
creating it
if not found in the underlying storage mechanism.

This is the central operation of a Scope, and the only operation
that is absolutely required.

Parameters:

name - the name of the object to retrieve

objectFactory - the ObjectFactory to use to create the scoped
object if it is not present in the underlying storage mechanism

Returns:

the desired object (never null)

Throws:

java.lang.IllegalStateException - if the underlying scope is not currently active

remove

java.lang.Object remove(java.lang.String name)

Remove the object with the given name from the underlying scope.

Returns null if no object was found; otherwise
returns the removed Object.

Note that an implementation should also remove a registered destruction
callback for the specified object, if any. It does, however, not
need to execute a registered destruction callback in this case,
since the object will be destroyed by the caller (if appropriate).

Note: This is an optional operation. Implementations may throw
UnsupportedOperationException if they do not support explicitly
removing an object.

Parameters:

name - the name of the object to remove

Returns:

the removed object, or null if no object was present

Throws:

java.lang.IllegalStateException - if the underlying scope is not currently active

registerDestructionCallback

Register a callback to be executed on destruction of the specified
object in the scope (or at destruction of the entire scope, if the
scope does not destroy individual objects but rather only terminates
in its entirety).

Note: This is an optional operation. This method will only
be called for scoped beans with actual destruction configuration
(DisposableBean, destroy-method, DestructionAwareBeanPostProcessor).
Implementations should do their best to execute a given callback
at the appropriate time. If such a callback is not supported by the
underlying runtime environment at all, the callback must be
ignored and a corresponding warning should be logged.

Note that 'destruction' refers to automatic destruction of
the object as part of the scope's own lifecycle, not to the individual
scoped object having been explicitly removed by the application.
If a scoped object gets removed via this facade's remove(String)
method, any registered destruction callback should be removed as well,
assuming that the removed object will be reused or manually destroyed.

Parameters:

name - the name of the object to execute the destruction callback for

callback - the destruction callback to be executed.
Note that the passed-in Runnable will never throw an exception,
so it can safely be executed without an enclosing try-catch block.
Furthermore, the Runnable will usually be serializable, provided
that its target object is serializable as well.

Throws:

java.lang.IllegalStateException - if the underlying scope is not currently active

resolveContextualObject

Resolve the contextual object for the given key, if any.
E.g. the HttpServletRequest object for key "request".

Parameters:

key - the contextual key

Returns:

the corresponding object, or null if none found

Throws:

java.lang.IllegalStateException - if the underlying scope is not currently active

getConversationId

java.lang.String getConversationId()

Return the conversation ID for the current underlying scope, if any.

The exact meaning of the conversation ID depends on the underlying
storage mechanism. In the case of session-scoped objects, the
conversation ID would typically be equal to (or derived from) the
session ID; in the
case of a custom conversation that sits within the overall session,
the specific ID for the current conversation would be appropriate.

Note: This is an optional operation. It is perfectly valid to
return null in an implementation of this method if the
underlying storage mechanism has no obvious candidate for such an ID.

Returns:

the conversation ID, or null if there is no
conversation ID for the current scope

Throws:

java.lang.IllegalStateException - if the underlying scope is not currently active